N20 is the most frequently used general anesthetic and inhalational sedative in medicine and dentistry. Since its discovery over 100 years ago, it has had an excellent record of safety. However, in recent years N20 has been shown to induce a variety of adverse health effects including a polyneuropathy following repeated subanesthetic exposures, significantly increased incidences of spontaneous abortions following trace exposures during pregnancy, increased incidences of liver, kidney and neurologic diseases following trace exposure to adults and megablastic bone marrow changes following prolonged high concentration (50%) exposure. Preliminary studies in our laboratory have indicated that N20 also displays a behavioral teratologic effect. Timed pregnant Sprague-Dawley rats were exposed to 75% N20/25% 02 or air for 8 hours late in pregnancy (Day 15). Litter size, birth weights and sex ratios of the offspring were unaffected by this treatment. However, behavior testing, using residential maze activity and time-lapse photography, indicate that the prenatal N20 exposed animals had radically altered behaviors as they matured. The present proposal plans to characterize this finding and determine a possible mechanism. The first studies will determine if exposure to N20 during early development or as adults produces similar changes in behavior. Secondly, the possibility that other CNS depressants used in anesthesia, such as fluothane and pentobarbital, have similar teratogenic properties will be investigated. Careful teratogenic screening of morphologic and biochemical effects of late pregnancy exposure to N20 will be carried out. Finally, N20's known property of vitamin B12 inactivation, will be studied as a possible mechanism for its behavioral toxicity by evaluating behavior, folic acid metabolism, DNA and protein content following prenatal exposure to N20 of animals pretreated with folinic acid.